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Applying Feedback Control to QoS management

Applying Feedback Control to QoS management. - an introduction -. Giovanna.Ferrari@ncl.ac.uk. Outline. Focus. Use of Feedback Control Theory in computing systems for QoS management

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Applying Feedback Control to QoS management

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  1. Applying Feedback Control to QoS management - an introduction - Giovanna.Ferrari@ncl.ac.uk

  2. Outline Focus Use of Feedback Control Theory in computing systems for QoS management To apply theory to govern component execution in the scope of the TAPAS project, addressing the goal of developing Trusted and QoS-aware middleware services for Application Hosting • Control Theory • Feedback Control • Middleware for QoS Control • Conclusions Motivation

  3. Example: in an e-business server, neither the resource requirements nor the arrival rate of service requests are known a priori Problem: difficulty meeting performance guarantees, failure may result in loss of customers and financial damage Solution: a well developed analytic foundation for performance control in physical systems based on Control Theory Dynamic Systems and Control Theory Application over Internet: Dynamic System living in an ever changing environment, it evolves over the timeand nothing is known a priori Subject: soft real-time applications executing in open and unpredictable environments

  4. Control Theory The objective in a Control System is to make some output behave in a desired way by manipulating some input,employing differential equations as a fundamental modelling tool • Success: due to its robustness in the face of modelling errors and external disturbances, which reduces the need for accurate system models • Recent results:Control Theory in Computing Systems • Network flow controllers (TCP/IP), C. Hollot et al. (U.Mass) • Lotus Notes admission control, N. Gandhi et al. (IBM) • QoS in Caching, Y. Lu et al. (U.Virginia) • Performance guarantees for Apache , T. Abdelzaher et al. Control Theory

  5. Control System ENVIRONMENT Control System thermostat Represented by a controlled system in combination with a controller, their interactions are observations and manipulations performed by the controller on controlled system. control information CONTROLLER manipulation observation • Example: In a water heater, if the temperature drops below a set value, a constant heat source is switched on, to be switched off again when the temperature rises above a set maximum CONTROLLED SYSTEM input output cold water hot water water heater CONTROL SYSTEM BOILER

  6. Control System Strategies • Feed forward control strategymanipulation through control actions is determined based on observation of the input to the controlled system • A priori workload knowledge, a combination of pre­run­time analysis and admission control algorithms ensure that the system is not overloaded and that the desired performance is achieved • Feedback controlstrategy measurements of the output delivered are compared with a desired behaviour (reference) and the difference (error) is used to decide on the control actions to be taken • Applied for behaviour optimisation, it regulates control actions according to continuous performance feedback

  7. Feedback Control System The Controllercompares the performance reference with controlled variable to get the current error, and it calls a control algorithm to compute the control input, new value of the manipulated variable based on the error The Actuatorchanges the manipulated variable based on the newly computed control input CONTROLLED SYSTEM FEEDBACK CONTROL LOOP CONTROLLER control algorithm control input manipulated variable ACTUATOR error sample controlled variable SENSOR + - The Sensor measures the controlled variable and feeds the sample back to the Controller reference

  8. Feedback Control Continuous monitoring of the controlled system, comparing the actual behaviour result against a specification of the expected behaviour and adjusting the performances accordingly Design challenges: • To develop a general methodology for converting specifications of a computing system into feedback loops with known set points and feedback control parameters. • To find a convenient interface between the service software and the middleware control loops that manage its performance. • To design appropriate software performance sensors and actuators. Feedback Control

  9. Feedback Control • Performance-assured services (e-commerce, online trading) • Services differentiation • Contractual satisfaction guarantees • Overload control Potential applications: E-COMMERCE PRICING CLIENT HETEROGENEITY NETWORK QoS SERVER OVERLOAD MULTIMEDIA

  10. Feedback Control Related works: • AMIDST:architecture to support QoS-aware m/w, focusing on the QoS-control system. An architectural framework, based on models from Control Theory, observes and manipulates the state of the m/w platform that supports distributed applications • CONTROLWARE:m/w architecture for QoS guarantees in distributed environments. It implements a new paradigm for QoS control, suitable for system operating in highly uncertain environments or when accurate system load and resource models are not available

  11. Middleware for QoS Control Diagram of a model APPLICATIONS agreed QoS difference COMPARATOR measurement (QoS state) DECIDER control strategy INTERPRETER TRANSLATOR observation control action SENSOR ACTUATOR probe probe MIDDLEWARE PLATFORM COMPUTING & COMMUNICATION RESOURCES input output

  12. Middleware for QoS Control Middleware for QoS Control monitors the output and reconfigures itself to provide the application with a stable execution environment • Adaptation based middleware architecture demands three principal stages of run time support: • probingthe performance of QoS parameters • instantiatingthe initial middleware configuration • adapting to on-the-fly variations TAPAS Project:Trusted and QoS-aware middleware services for Application Hosting

  13. Conclusions Applying Feedback Control to QoS management • Feedback Control Theory offers a valid solution to achieve performance guarantees for soft real-time applications • Successfully applied by the engineering community in controlling a vast variety of physical systems • Recent results prove that Control Theory can also be efficiently applied to the control of software performance • Theoretical basis for the design of a QoS aware middleware

  14. Selected bibliography • MODERN CONTROL SYSTEMS, R.Dorf, R.Bishop, Prentice Hall • ControlWare: A Middleware Architecture for Feedback Control of Software Performance, R. Zhang, C.Lu, Tarek F. Abdelzaher, John A. Stankovic(Department of Computer ScienceUniversity of Virginia - 2002) • SWiFT: A Feedback Control and Dynamic Reconfiguration Toolkit A.Goel, D.Steere, C.Pu, J.Walpole,(Department of Computer Science and EngineeringOregon Graduate Institute, Portland - 1999) • AMIDST: A QoS-Control Architecture for Object Middleware, L.Bergmans, A.van Halteren, L.Ferreira Pires, M.van Sinderen and M.Aksit,(CTIT University of Twente, The Netherlands - 2000)

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